1. Field of the Invention
The present invention relates to a vehicle generator controller for gradually increasing the current generated by a generator by gradually increasing a field current by intermittently operating a switching element when a battery voltage is dropped by the turn-on of an electric load, and more specifically, to a vehicle generator controller by which the cyclic drop of the battery voltage is suppressed when the electric load is repeatedly turned on and off.
2. Description of the Related Art
Conventionally, in a vehicle generator controller, since a torque shock is caused when a generated current is increased in instant response to the drop of a battery voltage, the current generated by a generator is gradually increased by gradually increasing a field current by the gradual increase of a conducting ratio (duty) executed by the intermittent operation of a switching element.
FIG. 2 is a circuit diagram showing a conventional vehicle generator controller disclosed in, for example, Japanese Unexamined Utility Model Publication No. 64-34900.
In the drawing, a generator 1 driven by an internal combustion engine (not shown) includes an armature coil 101 and a field coil 102 and is mounted on a vehicle.
The rectifier 2 of the generator 1 for subjecting the ac output from the generator 1 to full wave rectification includes an output terminal 201 acting as the main output terminal of a generated voltage VG, an output terminal 202 for exciting the field coil 102 and an output terminal 203 for the ground.
A controller for controlling the field current IF (generated current IG) of the generator 1 is composed of a voltage regulator 4 for regulating the output voltage VG (battery voltage VB) from the generator 1 to a predetermined value, a smoothing circuit 5 for smoothing the voltage detecting signal D of the battery voltage, a comparison circuit 7 operating in response to the output signal level from the smoothing circuit 5 and a constant voltage power supply circuit 8 for creating a constant power source A.
The smoothing circuit 5 and the comparison circuit 7 constitute a gradual increase control circuit for gradually increasing the field current IF of the generator 1 when the battery voltage VB drops.
A battery 9 mounted on the vehicle is charged by the output created by the generator 1 through the rectifier 2. A key switch 10 is connected to an end of the battery 9. The electric load 11 of the vehicle such as head lights, an air conditioner and the like is connected between both the ends of the battery 9. A switch 12 for imposing the electric load 11 is inserted between an end of the electric load 11 and one of the ends the battery 9.
The voltage regulator 4 includes resistors 401, 402 for creating a detected voltage Vb by dividing the voltage VB of the battery 9, resistors 403, 404 for creating a reference voltage VR by dividing the constant power source A, a comparator 405 for outputting a voltage detection signal D by comparing the detected voltage Vb with the reference voltage VR, an emitter-grounded transistor 407 inserted to the field coil 102 in series therewith for intermittently controlling the field current IF, a diode 408 for absorbing the surge caused by the intermittent operation of the transistor 407 and a resistor 409 inserted between the base of the transistor 407 and the output terminal 202.
The voltage regulator 4 includes an emitter-grounded transistor 410 having a collector connected to the base of the transistor 407, a pair of diodes 411, 412 inserted in series between the output terminal of the comparator 405 and the base of the transistor 410 in inverted polarity and a resistor 413 inserted between the constant power source A and the point where diode 411 is connected to the diode 412.
The smoothing circuit 5 includes a pair of diodes 511, 512 connected in series to the output terminal of the comparator 405 in inverted polarity, a charging resistor 513 inserted between the constant power source A and the point where the diode 511 is connected to the diode 512, a capacitor 503 inserted between the cathode of the diode 512 and the ground and a discharging resistor 515 connected in parallel with the capacitor 503.
The comparison circuit 7 includes a comparator 702 for outputting a gradual increase control signal E by comparing a triangle voltage VT created from a triangle generator 701 with the capacitor voltage VC from the capacitor 503, an emitter-grounded transistor 712 inserted between the base of the transistor 407 and the ground and a resistor 713 inserted between the point where the base of the transistor 712 is connected to the output terminal of the comparator 702 and the constant power source A.
With this arrangement, the comparison circuit 7 creates an intermittent control signal based on the gradual increase control signal E to thereby create an intermittent control signal F to the field coil 102 by the intermittent operation of the transistor 407, so that the comparison circuit 7 gradually increases the field current IF and the current generated by the generator 1.
The gradual increase control signal E which is output from the comparator 702 gradually increases the conducting duty of the transistor 407 in response to the voltage which is output from the smoothing circuit 5, that is, to the capacitor voltage VC to thereby gradually increase the field current IF.
A series circuit composed of a diode 111 and an initially exciting resistor 112 is inserted between the key switch 10 and an end of the field coil 102.
The constant voltage power supply circuit 8 is composed of a series circuit inserted between the key switch 10 and the ground and including a pull-up resistor 801 and a Zener diode 802.
With this arrangement, when the key switch 10 is turned on, the constant power source A is created from the point where the pull-up resistor 801 is connected to the Zener diode 802 based on the battery voltage VB.
Next, operation of the conventional vehicle generator controller shown in FIG. 2 will be described with reference to the waveform views of FIG. 3 and FIG. 4.
FIG. 3 and FIG. 4 show the change in time of respective signals D-F and respective voltages VB and VC as well as the current which is output from the generator, that is, the current IG generated therefrom which corresponds to the turning on and off of the electric load 11, wherein FIG. 3 is an operation waveform view when the head lights, defoggers and the like which are usually in an on-state are turned on and FIG. 4 is an operation waveform view when a hazard indicator, a winker and the like which are intermittently imposed are turned on.
In this case, since the charging resistor 513 in the smoothing circuit 5 has a relatively small resistance value and the discharging resistor 515 therein has a relatively large resistance value, a charging time constant is set to a short time of about 100 milliseconds and a discharging time constant is set long of about a few seconds.
Further, it is assumed that the voltage detection signal D from the comparator 405 and the gradual increase control signal E from the comparator 702 exhibit an approximately equivalent operation waveform in the usual state that the electric load 11 is not turned on.
First, when the key switch 10 is turned on, the battery voltage VB of the battery 9 is imposed on the Zener diode 802 through the resistor 801 and the constant power source A which is clamped by the Zener diode 802 is created from the point where the resistor 801 is connected to the Zener diode 802.
With this operation, although the controller of the generator 1 is made to an operable state, since the generator 1 does not yet start power generation, the signal level on the non-inverting input terminal (+) side of the comparator 405 in the voltage regulator 4 is lower than the reference voltage VR on the inverting terminal (-) thereof and accordingly the comparator 405 outputs the voltage detection signal D of a level.
At the time, since the capacitor 503 in the smoothing circuit 5 is not charged, the capacitor voltage VC has a zero potential. Therefore, the signal level on the non-inverting input terminal (+) side of the comparator 702 in the comparison circuit 7 is lower than the triangle voltage VT and the gradual increase control signal E is fixed to a low level and the transistor 712 remains in an off-state.
Consequently, the transistor 407 is turned on and the field current IF flows to the field coil 102 to thereby put the generator 1 to a power generation possible state.
When the internal combustion engine starts operation and the generator 1 starts power generation by being driven by the internal combustion engine, the signal level on the non-inverting input terminal (+) side of the comparator 405 in the voltage regulator 4 is increased by the increase of the battery voltage VB. When the signal level on the non-inverting input terminal (+) side becomes higher than the reference voltage VR, the voltage detection signal D is switched from the low level to a high level and the transistor 407 is switched from a conducting state to a shut-off state.
As described above, the voltage regulator 4 detects the battery voltage VB at all times and when, for example, it detects the drop of the battery voltage VB, it increases the conducting ratio of the transistor 407 through the comparator 702.
Since the field current IF is increased by the increase of the conducting ratio of the transistor 407 and the battery 9 is charged by the increase of the output from the generator 1, the battery voltage VB is controlled to a constant rated voltage.
When, for example, the switch 12 is turned on and the electric load 11 is turned on, the comparator 702 is operated and the field current IF is increased by the drop of the battery voltage VB.
At the time, although the comparator 405 which responds to the battery voltage VB creates the voltage detection signal D of a low level by increasing the conducting duty of the field current IF, since the discharging time constant of the smoothing circuit 5 is set longer than the charging time constant thereof, the comparator 702 in the comparison circuit 7 increases the conducting ratio of the transistor 407 so as to gradually increase the duty.
Therefore, as the conducting ratio of the transistor 407 increases, the field current IF gradually increases so that the output from the generator 1 gradually increases while suppressing a response shock.
When, for example, the usually-turned-on electric load 11 (head lights, defoggers and the like) is turned on, the voltage detection signal D intends to increase the conducting duty by becoming to the low level when the electric load 11 is turned on as shown in FIG. 3. However, since the capacitor voltage VC is dropped by the long time constant and the duty of the low level section of the gradual increase control signal E is gradually increased, the generated current IG is gradually increased while being suppressed without reaching a value corresponding to the response at once.
At the time, the battery voltage VB temporarily drops by a drop amount VB when the electric load 11 is turned on.
Further, when the electric load 11 is turned off because the switch 12 is shut off, since the voltage detection signal D of the high level which is output from the comparator 405 is imposed on the transistor 407, the intermittent control signal F is made to an operation waveform equivalent to the voltage detection signal D which relatively promptly returns to the waveform before the electric load 11 is turned on.
At the time, since the charging time constant determined by the resistor 513 and the capacitor 503 in the smoothing circuit 5 is short and the capacitor voltage VC is promptly charged as shown in the drawing, the gradual increase control signal E from the comparator. 702 also relatively promptly returns to the waveform (waveform in the low level section having a small duty) before the electric load 11 is turned on.
Likewise, when the electric load 11 (hazard indicator, winker and the like) which is intermittently imposed is turned on, the battery voltage VB also temporarily drops by the drop amount VB when the electric load 11 is turned on as shown in FIG. 4.
Thereafter, when the electric load 11 is turned off in the cyclic turning on and off thereof, the gradual increase control signal E which is output from the comparator 702 returns to the waveform before the electric load 11 is turned on.
At the time, since the gradual increase control signal E promptly returns to the waveform before the electric load 11 is turned on as described above when the electric load 11 is turned off, the battery voltage VB also temporarily drops by the drop amount VB when the electric load is turned on next time likewise the time when it was turned on for the first time.
Therefore, since the battery voltage VB cyclically drops each time the electric load 11 is repeatedly turned on in the case of FIG. 4, the head lights which have been turned on lower their quantity of light cyclically, by which the driver is made uncomfortable.
As described above, although the conventional vehicle generator controller gradually increases the field current (generated current) by the gradual increase control circuit composed of the smoothing circuit 5 and the comparison circuit 7 so as to suppress the torque shock when the electric load 11 is turned on, since the charging time constant is set short, the capacitor 503 is the smoothing circuit 5 is charged in a short time when the electric load 11 is turned off. Thus, there is a problem that when, in particular, the electric load 11 is repeatedly turned on and off, the battery voltage VB greatly drops each time the electric load 11 is turned on, by which the driver is made uncomfortable.
An object of the present invention made to solve the above problem is to provide a vehicle generator controller for suppressing a torque shock which is caused in response to the turn-on of an electric load as well as suppressing the drop of a battery voltage when the electric load is repeatedly turned on.